CN114559861A

CN114559861A - Fuel cell vehicle and control strategy based on artificial battery discharge limit

Info

Publication number: CN114559861A
Application number: CN202111408102.3A
Authority: CN
Inventors: 陈瀚点; 乌尔斯·克里斯汀
Original assignee: Ford Global Technologies LLC
Current assignee: Ford Global Technologies LLC
Priority date: 2020-11-27
Filing date: 2021-11-24
Publication date: 2022-05-31
Also published as: DE102020214928A1; US20220169150A1

Abstract

A vehicle and method of operating a vehicle having a powertrain including a fuel cell device and a traction battery includes setting an upper threshold for traction battery output power, determining a current maximum possible power request, determining an output power currently available to the fuel cell device, determining an output power currently available to the traction battery based on the upper threshold, and adjusting the upper threshold for the allowable output power of the traction battery based on the determined current maximum power request, the output power currently available to the fuel cell device, and the output power currently available to the traction battery.

Description

Fuel cell vehicle and control strategy based on artificial battery discharge limit

Technical Field

The present disclosure relates to a fuel cell vehicle and a control strategy.

Background

The fuel cell device is characterized by a significantly reduced dynamic behavior compared to conventional internal combustion engines. This means that in the case of a power request by the fuel cell controller, it may take several seconds to deliver the required power. For this reason, fuel cell vehicles are equipped with a drive battery or a traction battery so that the power request can be met by the battery in a short time while the fuel cell apparatus is gradually started (ramp up). However, due to slow response dynamics, an undesirable delay in providing drive power may occur, especially if the battery reaches a maximum discharge power or output power.

In the case of vehicular applications, it is well known that fuel cell devices may not be able to meet the typical high dynamic power requests of users. Therefore, fuel cell vehicles are typically equipped with traction batteries to meet short term power requests. However, the power supplied by the battery is limited by the discharge limit, which is why the power is often not sufficient to cover the entire power request to accelerate the vehicle in all situations, in contrast to battery-driven vehicles with significantly larger batteries. Due to the power limit that allows the battery to discharge and the slow response dynamics of the fuel cell device, there is a significant delay in providing the requested power under certain acceleration conditions, particularly where the power request is not properly distributed between the fuel cell and the battery.

Document DE 102014215160 a1 describes a method for controlling an electric machine of a fuel cell vehicle having a fuel cell and a battery, wherein the load division between the fuel cell and the battery is carried out as a function of a drive power request variable and on the basis of load sharing information. In particular, thermal aspects and cooling requirements are considered. Documents us8,080,971b2, us9,020,799b2, us9,649,951b2 and US7,954,579B2 describe further state of the art with respect to meeting power requests by an energy device of a fuel cell powered vehicle. The prior art regarding the application of game theory in the control of hybrid electric vehicles can be found in: C.Dextreit and I.Kolmanovsky, door the Control for hybrid electric vehicles, IEEE Transactions on Control Systems Technology, Vol.22(No.2): pp.652-663, March 2014.

Disclosure of Invention

Against this background, one or more embodiments of the subject matter of the application provide a vehicle operating a powertrain having a fuel cell plant and a traction battery, wherein in particular a short-term or temporary power request can be fully fulfilled in a short time. The subject matter of the application relates to operating a fuel cell arrangement such that, based on a defined upper threshold value for allowed output power, excess power and unused battery power of the fuel cell arrangement are utilized in such a way that the sum of the available power at a particular time or in a particular situation corresponds to the maximum possible power request of a user at the respective time or in the respective situation.

In one or more embodiments, a method of operating a vehicle according to the present disclosure relates to a vehicle having a powertrain including a fuel cell device and a traction battery. The method includes setting an upper threshold for allowable output power of the traction battery. A current maximum possible power request is determined. The current available output power of the fuel cell device is determined. The current available output power of the traction battery is determined (according to an upper threshold of allowable output power). The determination of the current maximum possible power request, the determination of the current available output power of the fuel cell device and the current available output power of the traction battery may be performed simultaneously or in any order. The upper threshold value for the allowable output power of the traction battery is then adjusted in accordance with the specified current maximum possible power request, the current available output power of the fuel cell device and the current available output power of the traction battery. After adjusting the upper threshold in the method, the power can be output by the fuel cell device and/or by the traction battery.

The flexible adjustment of the upper threshold value for the permissible output power of the traction battery according to the above-described method has the advantage that the traction battery can be charged for a short time by the power surplus of the fuel cell device or, if necessary, the power reserve of the traction battery can be used to meet temporary power requests.

In an advantageous variant, the upper threshold value for the permissible output power of the traction battery is adjusted such that the sum of the currently available output power of the fuel cell arrangement and the currently available output power of the traction battery reaches the current maximum possible power request determined as a function of the upper threshold value for the permissible output power of the traction battery. This ensures that the possible output powers of the fuel cell system and the traction battery are divided in such a way that the maximum power request expected in each case is also fulfilled at this time.

The current maximum possible power request may be determined as a function of the power request input (e.g., the engagement state of the accelerator pedal). Additionally or alternatively, the current maximum possible power request may also be determined based on characteristics of the traveled route and/or the current route and/or the route to be traveled. For this purpose, data from the navigation device and/or cloud-based data and/or data about traffic conditions may be used. These variants make it possible to reliably and efficiently predict potential power requests and to ensure a suitable output power when a corresponding power request occurs.

In another additional or alternative variant, the current maximum possible power request may be determined from characteristics characterizing the driving style. The driving style may be derived, for example, from the current and/or previous driving behavior of the user or from a setting of an operation mode, such as a sporty operation mode, a comfortable operation mode or an energy saving operation mode. The characteristics of the traveled route and/or the current route and/or the route to be traveled and/or the characteristics characterizing the driving style may be recorded and/or evaluated, for example analyzed.

Furthermore, the upper threshold value of the allowable output power of the traction battery may be adjusted according to the temperature of the traction battery. This makes it possible to take into account and use fluctuations in the traction battery output power as a function of temperature.

The traction battery may be charged by the fuel cell device if the current power request is below the determined current maximum possible power request. This makes it possible to reduce the delay in power output when a sudden high power request occurs. By operating the fuel cell device accordingly, in the event of a power request, the traction battery can be charged in advance to a level that allows the maximum power request to be met in the short term by the combination of the traction battery and the output power of the fuel cell device.

Advantageously, in the case of a power request input, the proportion of the power which the traction battery needs to output to the total power to be output (i.e. the total power required to reach or satisfy the power request input) and the proportion of the power which the fuel cell device needs to output to the total power to be output depend on the dynamics of the currently possible output power of the fuel cell device. This makes it possible to satisfy high transient power requests by means of a clever partitioning and, if necessary, temporary charging of the traction battery.

In a further variant, in the case of a power request input, the power request of the traction battery is determined before the power request of the fuel cell system is determined from the adjusted upper threshold value for the permissible output power of the traction battery and/or the power request of the traction battery. This has the advantage that the power request of the fuel cell device can be determined from the state of charge of the traction battery and the additional charging that may be required. In other words, this sequence allows the traction battery to be charged by the fuel cell device to adequately meet the upcoming power request.

The power request of the fuel cell device may be determined (e.g., calculated) based on the current state of charge of the traction battery and/or the power request of the traction battery (e.g., determined traction battery power request). In particular, the power request of the traction battery may be determined by: it is below the upper threshold of allowed output power minus the difference between the maximum rated power and the power requested by the user. The power request of the fuel cell device may be determined as the difference between the total power currently requested by the user and the determined traction battery power request.

In an advantageous variant, the dynamics of the current output power of the fuel cell device and/or the upcoming power request (in particular the total power request) of the user can be modeled and/or determined on the basis of a model. In particular, methods using game theory and/or non-linear models may be used. In this way it is possible to identify upcoming power requests that are tailored to a particular situation and to predict the user's behavior and fully satisfy them in time.

In a further variant, the adjustment of the upper threshold value for the permissible output power of the traction battery can be repeated after the expiration of a specified time, for example after the expiration of a time of 10 to 100 milliseconds. The adjusted threshold sum may be stored in a look-up table in a memory accessible to the vehicle controller. The adjusted threshold lookup table may be indexed or accessed by one or more parameters that are the basis for the adjustment. Such as the power requested by the user, characteristics of the route, characteristics characterizing the driving style of the user, and the temperature of the traction battery. For example, the table may be one-dimensional, two-dimensional, or multi-dimensional.

The control device for a vehicle drive comprising a fuel cell device and a traction battery is designed to carry out the method according to the foregoing. The control device may have an evaluation unit for adjusting an upper threshold value of the permissible output power of the traction battery. It may also have means for determining the output power of the traction battery and the output power of the fuel cell device in the case of a power request. It may also include other devices or means necessary to perform one or more of the above-described steps of the method.

The vehicle includes a drive with a fuel cell device and a traction battery. The vehicle further comprises the control device described earlier. The vehicle may be, for example, a motor vehicle, a rail vehicle or a ship. The motor vehicle may be, for example, a passenger car, a truck, a bus, a mini-bus, an electric vehicle, or a motorcycle.

A computer-implemented method includes instructions that, when executed by a computer, cause the computer to perform the method described above. A computer program product comprises instructions which, when the program is executed by a computer, cause the computer to carry out the above-mentioned method. The computer program product or computer-readable storage medium contains instructions which, when executed by a computer, cause the computer to carry out the method as described above.

The subject matter of the application is explained in more detail below on the basis of representative embodiments with reference to the drawing. While representative embodiments have been illustrated and described in greater detail, the subject matter of the application is not limited by the disclosed examples, and other variations from the examples can be derived by those skilled in the art without departing from the scope of the subject matter of the application.

The drawings are not necessarily to scale, and may be exaggerated or minimized to provide a better overview. Therefore, the functional details disclosed herein are not to be interpreted strictly, but merely as a basis for teaching one skilled in the art to variously employ the disclosed techniques.

As used herein, the term "and/or," when used in reference to a series of two or more elements, means that each of the listed elements can be used alone or in any combination of two or more of the listed elements. For example, if a composition is described that contains components A, B and/or C, such composition may contain a alone; b alone; c alone; a and B in combination; a and C in combination; b and C in combination; or a combination of A, B and C.

Drawings

Fig. 1 schematically shows an example of the variation of the propulsion power of a drive comprising a fuel cell arrangement and a traction battery over time in a diagram;

FIG. 2 schematically shows in a graph the output power of the fuel cell apparatus of FIG. 1 as a function of time;

FIG. 3 schematically illustrates in a graph the output power of the traction battery of FIG. 1 as a function of time;

fig. 4 shows schematically in a diagram the variation over time of the drive power of a drive comprising a fuel cell device and a traction battery;

FIG. 5 schematically shows in a graph the output power of the fuel cell apparatus of FIG. 4 as a function of time;

FIG. 6 schematically illustrates in a graph the output power of the traction battery of FIG. 4 as a function of time;

FIG. 7 schematically shows a method according to the invention in a flow chart;

FIG. 8 schematically illustrates an energy management decision process;

FIG. 9 schematically illustrates an energy management decision process;

fig. 10 schematically shows a change in power request of output power of the fuel cell apparatus with time;

fig. 11 schematically shows a motor vehicle with a control device of the present disclosure.

Detailed Description

As required, detailed embodiments are disclosed herein; however, it is to be understood that the disclosed embodiments are merely representative and may be embodied in various and alternative forms. The figures are not necessarily to scale; some features may be exaggerated or minimized to show details of particular components. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a representative basis for teaching one skilled in the art to variously employ the claimed subject matter.

First, fig. 1 to 3 are diagrams for explaining an initial case to explain a general procedure by way of example. Fig. 1 shows the variation of the propulsion power P of a drive comprising a fuel cell and a traction battery over time t. The drive power is given in kilowatts (kW) and the time axis in arbitrary, numerically unspecified units. Fig. 2 schematically shows the output power of the fuel cell apparatus as a function of time. Fig. 3 schematically shows the output power of the traction battery as a function of time.

In the example shown, the user may require a nominal drive power of 100 kW. If the driver is powering the vehicle at time t0 using 20kW and the current upper limit of power that the traction battery may be delivering is 50kW, the energy management strategy employed may decide that the request for motive power is fully met by the traction battery and the fuel cell arrangement remains off. However, if the driver depresses the accelerator pedal and suddenly requests a power output of 80kw, the output power of the traction battery can only be increased to 50kw, and the resulting power gap of 30kw can only be compensated by the fuel cell arrangement. However, the corresponding output power can only be output after a delay of a few seconds. This is depicted in fig. 1 to 3.

From time t0 time t1, 20 kilowatts of power are used to drive the vehicle. At time t1, the power request is 80 kw. The power request is characterized by curve 1. The possible total output over time is characterized by curve 2. The output power of the traction battery is characterized by curve 3 and the output power of the fuel cell device by curve 4. In fig. 1, reference numeral 3 merely refers to the curve labeled with it before time t 2. Curve 5 represents the sum of the output powers of the traction battery and the fuel cell device.

The output power of the traction battery is increased from 20kW to 50kW due to the power request at time t 1. Subsequently, the fuel cell device does not start outputting or distributing power until time t 2. Between times t2 and t3, the output power of the fuel cell device is increasing, thus meeting the original 80kw power request at time t 3. From time t3, the power request is satisfied with further increased output power of the fuel cell device while the proportion of the traction battery output power is reduced.

However, if in this case the energy management system provides the original 20kw of power required for propulsion by the fuel cell arrangement, i.e. is required between times t0 and t1, and during this time the traction battery is charged an additional 30kw, the user can at any time call for or demand the full 100kw of rated power. Thus, the user can be immediately provided with the required 80kw driving power. Over time, as power is required, the fuel cell device can provide more power, and thus the power provided by the traction battery can be reduced. The traction battery may also be prepared in this manner for future use.

The above-described process is illustrated in fig. 4 to 6. Fig. 4 shows the variation of the drive power P of the driver over time t. The sum of the output powers of the traction battery and the fuel cell device is marked with reference number 5. Fig. 5 schematically shows the variation of the output power of the fuel cell apparatus with time. Fig. 6 schematically shows the output power of the traction battery as a function of time.

Between times t0 and t1, 50 kilowatts of power are emitted by the fuel cell device. Where 20 kilowatts are used to drive the vehicle and 30 kilowatts are used to charge the traction battery. At time t1, a power request time of 80kw, 50kw is provided by the fuel cell device and 30kw is provided by the traction battery to meet the power request. From time t4, the proportion of power supplied by the fuel cell device is increasing and the power supplied by the traction battery is decreasing until the power required at time t5 is fully supplied by the fuel cell device, so that no further loading of the traction battery is required. By reducing the output power of the traction battery to 0kW at time t5, the state of charge of the traction battery is maintained at a level which makes it possible to provide a further power request of up to 100kW of drive power and also to charge the battery with the power provided by the fuel cell arrangement in the event of a release of the accelerator pedal or a sudden significant reduction in the drive power request.

Reaching rated power may be limited by traction battery temperature. For example, if the traction battery is cold or hot, it may not be possible to achieve sufficient discharge power. In this case, the power request is at least almost fulfilled by a method according to one or more embodiments of the present disclosure. In the case of a cold traction battery, charging the traction battery may be used to simultaneously heat the battery, increasing the potential output power over time.

Further limitations arise when the traction battery's state of charge reaches its upper limit and is therefore unable to be recharged. In this case, at least further charging has to be interrupted. In any case, the battery size should be selected in such a way that the upper threshold of allowable output power is at least selected so that the battery can meet all transient power requests at normal operating temperatures.

Fig. 7 schematically shows a method according to the invention in the form of a flow chart. In a first step 11, an upper threshold value of the allowable output power of the traction battery is set. In step 12, the current maximum possible power request is determined. In step 13, the current available output power of the fuel cell device is determined. In step 14, the current available output power of the traction battery is determined according to the upper threshold value of the allowable output power. Steps 12 to 14 may also be performed in a different order or simultaneously. Step 15 adjusts the upper threshold of the allowable output power of the traction battery. This is done depending on the determined current maximum possible power request, the current available output power of the fuel cell device and the current available output power of the traction battery. In step 16, the output power of the fuel cell device and the traction battery may be determined.

Preparing the maximum rated power at all times reduces efficiency. Thus, in another approach, the dynamics of the fuel cell device are taken into account and divided accurately between power that can be built up fast enough to meet user requests and power that cannot be delivered fast enough to potentially cause power gaps that cannot be quickly overcome in the energy-efficient mode of operation. This division is not constant but varies depending on the operating conditions and the operating state of the fuel cell apparatus.

Advantageously, the user's behavior is taken into account, for example by adaptively observing and evaluating the behavior when the accelerator pedal is pressed, released or adjusted, by observing and evaluating traffic conditions, for example by means of cloud-based information or by a combination of the above options. If, for example, it is known that the user or driver does not expect the entire power to be available for a short period of time, the energy management may be adapted according to various embodiments such that the corresponding power does not remain available at all times. The advantage is that the user can optimize the power available at any time by accurately estimating the fuel cell dynamics and correctly predicting the potential power request. In this way, on the one hand, overcharging of the battery is avoided, and on the other hand, any gaps in the drive power are also avoided.

Fig. 8 and 9 illustrate typical energy management decision processes. The power request is marked with reference numeral 21. The power request is forwarded to the means 22 for determining battery power and to the additional element 23. Depending on the available battery power, a battery power request 24 is issued to the add-on 23. The power request of the fuel cell system is determined and output by the additional element 23. This is a feature characterized by block 25.

Fig. 8 illustrates conventional steps, as well as fig. 1 to 3. Fig. 9 shows a process of a system or method according to one or more embodiments of the present disclosure. In this case, the method according to the present invention as shown in fig. 7 or fig. 4 to 6 is performed before the battery power request is output to the additional element. An upper threshold for the allowable output power of the traction battery is adjusted (indicated by block 26) and a battery power request 24 adjusted by the upper threshold is then output to the parasitic element 23.

The output battery power request Pbatt, represented by block 24, should not be greater than the upper threshold of the allowable output power Pdis. It should be less than the upper threshold of allowable output power minus the difference between the maximum rated power Pmax and the user's power request Pdr: pbatt < Pdis- (Pmax-Pdr). The power request of such a traction battery can also be negative, in which case the traction battery is first charged by means of the fuel cell device. This is a possible situation especially if the driver side power request is low. The battery power request does not have to be equated with a threshold for the permitted output power, it may be lower, so that the available power of the traction battery that may be used is freely selectable. Subsequently, as shown in fig. 8 and 9, the power request Pfc of the fuel cell apparatus for satisfying the power request is calculated: Pfc-Pdr-Pbatt.

In the context of the method according to various embodiments, the power request of the traction battery may be limited to a value below the adjustment threshold, i.e. eventually a determined artificial threshold, for the allowable output power of the traction battery, which may be below the current allowable output power threshold before the power request of the battery is subtracted from the power request of the driver to calculate the power request of the fuel cell device. The determination of such an adjusted allowed output power threshold should predict a given driving behavior by looking for a trade-off between the battery allowed output power threshold and the fuel cell power dynamics. One possibility for such a solution is to apply game theory methods, such as the one described in the above document, where the solution can be stored in real time in a table of the application.

To calculate the threshold for traction battery allowable output power, a model describing the response of fuel cell power to a certain power request may be employed. An example of this is shown in fig. 10. Fig. 10 shows the response behavior, i.e. the change over time of the output power of the fuel cell device for a power request. On the x-axis, time is given in seconds(s), with no numerical specification. On the y-axis, power P is given in kilowatts (kW), but no values are specified.

Line 31 depicts the power request and curve 32 depicts the output power of the fuel cell device over time. In general, linear models are used to describe dynamics, i.e. in this case the increase in output power over time, but the game theory approach is also applicable to non-linear models. For example, in other linear models the time constant may depend on the operating point and the sign of the power change.

In the context of the game theory approach, the driver and traction battery are considered players who make decisions with opposite goals in the powertrain power balance. The power imbalance in the powertrain may be represented as Pimb ═ Pdr-Pbatt-Pfco |, where Pfco is the estimated output power of the fuel cell device, which is predicted from the power request Pfc of the fuel cell device using a model describing the dynamics of the fuel cell device (see fig. 10). Knowing the current output power of the fuel cell device, the driver tries to maximize the power imbalance of the driveline in the worst case and first selects a power request Pdr within the allowed range. In contrast, the traction battery responds to the driver's decision by selecting the requested battery power, Pbatt, within battery power limits with the goal of minimizing power imbalance in the powertrain. The resulting fuel cell power request Pfc is thus Pfc-Pdr-Pbatt.

These sequential decisions are made repeatedly within a given time window (typically on the order of seconds or fractions of a second). For real-time applications, this calculation is performed off-line, with the respective decisions of the traction battery being stored in a two-dimensional table. Therefore, in the table, the instantaneous drive power request and the instantaneous fuel cell output power are input data independently of each other. The output data of the two-dimensional table may be used as an adjusted upper threshold value for the allowable output power. As shown in fig. 9.

For further improvement, the optimization of the artificial battery discharge power limit may be based on the current actual maximum discharge power of the battery. Therefore, in this case, the table storing the optimization results must be extended by at least one input dimension, for example the current upper threshold of the allowable output power of the traction battery. It is also noted that the program can be further optimized by taking into account the most likely driving behaviour of the driver, knowing the driver and in particular the driving behaviour of the driver.

FIG. 11 schematically illustrates a motor vehicle 6 in accordance with one or more embodiments. The motor vehicle 6 comprises a drive 8 with a fuel cell device and a traction battery, and a control device 7, the control device 7 being designed to carry out the method described above.

In summary, the invention allows to shorten the response time of a powertrain comprising a fuel cell arrangement and a traction battery to a sudden power request, wherein the division between the power output by the fuel cell arrangement and the traction battery output power is optimized for reaching the desired power request.

While representative embodiments are described above, it is not intended that these embodiments describe all possible forms of the claimed subject matter. The words used in the specification are words of description rather than limitation, and it is understood that various changes may be made without departing from the claimed subject matter. Furthermore, the features of the various embodiments may be combined to form further embodiments of the claimed subject matter that are not explicitly illustrated or described.

Claims

1. A method of operating an electrified vehicle having an electric machine powered by a drivetrain that includes a fuel cell and a traction battery, the method comprising: performing, by a vehicle controller:

setting an upper threshold value of the allowable output power of the traction battery;

determining a current maximum possible power request;

determining the currently available output power of the fuel cell;

determining an output power currently available to the traction battery based on an upper threshold of allowable output power of the traction battery;

adjusting an upper threshold of the traction battery allowable output power according to the determined current maximum allowable power request, the current available output power of the fuel cell and the current available output power of the traction battery; and

controlling the traction battery and the fuel cell to power the motor according to the adjusted upper threshold.

2. The method of claim 1, wherein the upper threshold of traction battery permitted output power is adjusted such that the sum of the output power currently available to the fuel cell and the output power currently available to the traction battery corresponds to a current maximum permitted power request determined based on the upper threshold of traction battery permitted output power.

3. The method according to claim 1, wherein the current maximum possible power request depends on an input of a power request and at least one of characteristics of a traveled route, a current route, and a route to be traveled.

4. The method of claim 3, wherein characteristics of the traveled route, the current route, or the to-be-traveled route are stored in a memory accessible to the vehicle controller.

5. The method of claim 1, wherein the upper threshold is adjusted based on a temperature of the traction battery.

6. The method of claim 1, wherein the traction battery is charged by the fuel cell when a current power request is below a specified current maximum possible power request.

7. The method according to claim 1, wherein the proportion of the power to be output of the traction battery and the proportion of the power to be output of the fuel cell to achieve the power request depend on the dynamics of the output of the fuel cell.

8. The method of claim 7, wherein the dynamics of the output of the fuel cell is based on model values stored in a look-up table accessible to the vehicle controller.

9. The method of claim 1, wherein the adjusted upper threshold is retrieved from a lookup table stored in a memory accessible to the vehicle controller.

10. An electrified vehicle comprising:

a motor;

a traction battery configured to selectively transmit electrical energy to/from the electric machine;

a fuel cell configured to selectively provide electrical energy to the traction battery and the electric machine;

and the controller is programmed to adjust an upper threshold value of the output power of the traction battery according to the current maximum power request, the current available output power of the fuel battery and the current available output power of the traction battery, and control the traction battery and the fuel battery to supply power to the motor according to the upper threshold value.

11. The electrified vehicle of claim 10, wherein the controller is further programmed to adjust the upper threshold value according to an adjustment value stored in a lookup table stored in a memory accessible to the controller.

12. The electrified vehicle of claim 11, wherein the controller is further programmed to adjust the upper threshold such that a sum of an output power currently available to the fuel cell and an output power currently available to the traction battery corresponds to the determined maximum allowable power request.

13. The electrified vehicle of claim 12, wherein the controller determines the maximum allowed power request based on at least one of an input of a power request and a characteristic of a current route.

14. The electrified vehicle of claim 10, wherein the controller is programmed to adjust the upper threshold value as a function of a temperature of the traction battery.

15. The electrified vehicle of claim 10, wherein the controller is programmed to be present when

Charging the traction battery using electrical energy from the fuel cell when a previous power request is less than the current maximum power request.